Effector-dependent manipulation of host transcription is a key virulence mechanism used by Xanthomonas species causing bacterial spot disease in tomato and pepper. Transcription activator-like (
TAL) effectors employ novel
DNA-binding domains to directly activate host transcription, whereas the non-
TAL effector XopD uses a small
ubiquitin-like modifier (SUMO)
protease activity to represses host transcription. The targets of TAL and non-
TAL effectors provide insight to the genes governing susceptibility and resistance during Xanthomonas
infection. In this study, we investigated the extent to which the X. euvesicatoria non-
TAL effector strain Xe85-10 activates tomato transcription to gain new insight to the transcriptional circuits and virulence mechanisms associated with Xanthomonas euvesicatoria pathogenesis. Using transcriptional profiling, we identified a putative basic helix-loop-helix (
bHLH) transcription factor, bHLH132, as a pathogen-responsive gene that is moderately induced by microbe-associated molecular patterns and defense
hormones and is highly induced by XopD during X. euvesicatoria
infection. We also found that activation of bHLH132 transcription requires the XopD SUMO
protease activity. Silencing bHLH132
mRNA expression results in stunted tomato plants with enhanced susceptibility to X. euvesicatoria
infection. Our work suggests that bHLH132 is required for normal vegetative growth and development as well as resistance to X. euvesicatoria. It also suggests new transcription-based models describing XopD virulence and recognition in tomato.